WO2016056686A1

WO2016056686A1 - Signal transmission method for inter-cell interference

Info

Publication number: WO2016056686A1
Application number: PCT/KR2014/009416
Authority: WO
Inventors: 박경민; 조희정; 고현수; 최혜영; 변일무
Original assignee: 엘지전자 주식회사
Priority date: 2014-10-07
Filing date: 2014-10-07
Publication date: 2016-04-14
Also published as: US20170324526A1; US10230506B2

Abstract

A signal transmission method for reducing inter-cell interference according to the present invention may comprise the steps of: determining a rank on the basis of feedback information received from a terminal; generating a transmission sequence according to the rank; generating a repetitive transmission sequence by repeating the transmission sequence, and shifting a position of a symbol within the repetitive transmission sequence; and transmitting the transmission sequence and the repetitive transmission sequence. As a result, the present invention can implement an inter-cell interference randomization even in a closed-loop MINO.

Description

Signal transmission method for intercell interference

The present invention relates to wireless communication, and more particularly, to a signal transmission method and apparatus for inter-cell interference.

A transmission scheme based on orthogonal frequency division multiplexing access (OFDMA) may allocate one or more subcarriers independently to each terminal. Therefore, according to the request of the terminal, frequency resources can be efficiently allocated without intra-cell frequency interference.

In a cellular network system, the performance of the system may vary greatly depending on the position of the terminal in the cell. In particular, inter-cell interference can greatly degrade the performance of the UE located at the cell boundary. In addition, the higher the frequency reuse efficiency, the higher the data rate can be obtained in the cell center, but the inter-cell interference is more severe. Therefore, at the cell boundary, the signal-to-interference plus noise ratio (SINR) of the terminal may be more severely received due to the large interference from the adjacent cells.

In order to alleviate inter-cell interference in OFDMA-based cellular network systems, researches on avoiding inter-cell interference, averaging effects of inter-cell interference, and removing inter-cell interference have been conducted.

Currently, many moving cells exist in a cellular network system. Inter-cell interference may occur between the moving cell and the fixed cell. There is a need for a method for mitigating interference between moving cells and fixed cells.

One embodiment of the present invention provides a method and apparatus for mitigating intercell interference.

Another object of the present invention is to provide a method for generating a sequence for mitigating interference between cells and an apparatus using the same.

According to an embodiment of the present invention, a signal transmission method for mitigating intercell interference includes determining a rank based on feedback information received from a terminal; Generating a transmission sequence according to the rank; Repeating the transmission sequence to generate a repeating transmission sequence and shifting a position of a symbol within the repeating transmission sequence; And transmitting the transmission sequence and the repetitive transmission sequence.

The method may further include generating orthogonality between the transmission sequence and the repetitive transmission sequence by changing a phase of the repetitive transmission sequence with respect to the transmission sequence.

The pattern of repeated symbols in the repetitive transmission sequence may be determined according to a cell ID.

According to the present invention, a method and apparatus for mitigating intercell interference are provided.

According to the present invention, inter-cell interference between moving cells whose channel state changes rapidly based on precoding of a transmitting end can be alleviated. In detail, the averaging of the interference signal included in the reception signal of the receiver may be performed and faded out based on precoding of the transmitter, without performing an averaging for the interference at the receiver. In addition, interference for each of the plurality of received symbols may be randomized.

According to an embodiment of the present invention, a method for generating a sequence for mitigating intercell interference and an apparatus using the same are provided.

In addition, according to the present invention, a downlink closed-loop MIMO transmission technique is provided that overcomes randomization of unknown or unmeasured inter-cell interference.

1 is a diagram for a method of eliminating interference in a closed loop MIMO.

2 is a conceptual diagram illustrating a movement of a moving cell.

3 is a conceptual diagram illustrating a problem that occurs when interference between a moving cell and a fixed cell is controlled by a conventional inter-cell interference control scheme.

4 is a diagram illustrating an interference mitigation method according to an embodiment of the present invention.

5 is a diagram illustrating an interference mitigation method according to another embodiment of the present invention.

6 is a diagram illustrating repeatedly transmitting a signal through another channel.

7 is a diagram illustrating a symbol and an interference signal received through a quasi-static channel.

8 illustrates received symbols and interference signals according to an embodiment of the present invention.

9 is a diagram illustrating interference randomization according to a transmission signal of FIG. 8.

10 is a diagram illustrating the structure of a transmission stage according to an embodiment of the present invention.

11A illustrates a repeated transmission sequence according to an embodiment of the present invention.

11b illustrates a repeated transmission sequence according to an embodiment of the present invention.

11C is a diagram illustrating a repeated transmission sequence according to one embodiment of the present invention.

12 illustrates a transmission sequence in which a phase is changed according to an embodiment of the present invention.

13 is a diagram illustrating the structure of a transmission stage according to another embodiment of the present invention.

14 is a diagram for describing a repetition pattern allocated to a cell type according to one embodiment of the present invention.

15 is a diagram illustrating a signaling process for pattern change between base stations according to an embodiment of the present invention.

FIG. 16 illustrates a signaling process for pattern change between base stations according to another embodiment of the present invention.

17 is a block diagram of a wireless communication system according to an embodiment of the present invention.

The wireless device may be fixed or mobile and may be called other terms such as a user equipment (UE), a mobile station (MS), a user terminal (UT), a subscriber station (SS), a mobile terminal (MT), and the like. The terminal may be a portable device having a communication function such as a mobile phone, a PDA, a smart phone, a wireless modem, a laptop, or the like, or a non-portable device such as a PC or a vehicle-mounted device. . A base station generally refers to a fixed station for communicating with a wireless device, and may be referred to in other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like.

Hereinafter, the present invention will be applied based on 3rd Generation Partnership Project (3GPP) 3GPP long term evolution (LTE) or 3GPP LTE-A (LTE-Avanced). This is merely an example, and the present invention can be applied to various wireless communication systems. Hereinafter, LTE includes LTE and / or LTE-A.

The present specification describes a communication network, and the work performed in the communication network is performed in the process of controlling the network and transmitting data in a system (for example, a base station) that manages the communication network, or a terminal linked to the network. Work can be done in

Recently, commercialization of the LTE (Long Term Evolution) system, which is the next generation wireless communication system, is being supported in earnest. The LTE system is spreading more quickly after the need to support high-quality services for high-quality services as well as voice services while ensuring the activity of terminal users. The LTE system provides low transmission delay, high data rate, system capacity and coverage improvement.

Due to the emergence of such high quality services, the demand for wireless communication services is rapidly increasing. To cope with this actively, the capacity of the communication system must be increased.In order to increase the communication capacity in the wireless communication environment, a method of finding new available frequency bands and increasing the efficiency of limited resources can be considered. have.

In order to increase the efficiency of the limited resources among them, the transceiver is equipped with a plurality of antennas to obtain additional spatial area for resource utilization to obtain diversity gain or transmit data in parallel through each antenna. The so-called multi-antenna transmission and reception technology for increasing the capacity has been actively developed recently with great attention.

In a multiple-input multiple-output system, beamforming and precoding may be used as a method for increasing signal to noise ratio (SNR), and beamforming and precoding may use feedback information at a transmitter. In a closed-loop system, the feedback information is used to maximize the signal-to-noise ratio.

1 is a diagram for a method of eliminating interference in a closed loop MIMO.

As shown, the base station 1 may receive a feedback signal for a channel from each terminal 2 in the process of transmitting signals to the plurality of terminals 2.

When the base station 1 transmits a reference signal for channel state information (CSI) (S110), each terminal 2 measures the CSI (S120), and the measured CSI is measured by the base station 1 (S130).

The base station 1 may select a precoder for a signal based on the feedback information (S140) and transmit the precoded signal to the terminal 2.

As illustrated in FIG. 1, the base station 1 may transmit a signal generated in a spatial orthogonal manner to the terminal 2 (S150).

The terminal 2 may estimate a virtual channel with respect to the signal transmitted from the base station 1 (S160) and restore the signal (S170).

That is, in a closed loop MIMO system, a signal may be adjusted and transmitted so that a signal is transmitted only to a specific terminal desired based on channel information, and through this, internal interference and inter cell interference (ICI) may be eliminated.

By the interference cancellation method, interference by a plurality of user accesses (Multiple Access Interference, MAI) can be mitigated, and also interference can be minimized toward the antenna direction desired by the terminal through coordinated communication (Coordinated Multipoint, CoMP). have.

On the other hand, if the sharing of channel information between adjacent cells is not smooth, the inter-cell interference avoidance technique using the closed loop CoMP technique described above is difficult to apply. This is the case in which inter-cell interference occurs in a moving cell where a fast interface with a neighboring cell cannot be established at a fast time, or a femto cell in which information sharing with other cells is limited.

2 is a conceptual diagram illustrating a movement of a moving cell.

Hereinafter, in the embodiment of the present invention, the moving cell may indicate a base station moving, and a fixed cell may indicate a base station not moving at a fixed position. The moving cell may be expressed in other terms as the moving base station, and the fixed cell in other terms as the fixed base station.

For example, the moving cell 100 may be a base station installed in a moving object such as a bus. There may be about 2000 moving cells 100 based on the buses in Seoul. Therefore, there is a high possibility of interference between the moving cell 100 and the fixed cell 150 in the current cellular network system.

In the case of inter-cell interference between the fixed cells 150, resource division may be performed in consideration of the distance between the base station and the terminal to mitigate inter-cell interference. Alternatively, interference may be mitigated by dynamic resource division or cooperative communication by sharing channel information between cells.

However, in the case of the moving cell 100, it is difficult to use the interference control method between the fixed cells 150 as it is.

In moving cells, services through real-time traffic are often provided. Thus, interference control based on semi-static resource partitioning may be inappropriate in a moving cell.

Referring to the upper part of FIG. 3, the moving cell may be connected to another cell based on a wireless backhaul. Therefore, it may be difficult to perform dynamic resource partitioning by sharing channel information or use an inter-cell interference mitigation method based on cooperative communication. Specifically, in case of joint transmission (JT) / dynamic point selection (DPS), data to be transmitted to a terminal through a wired backhaul between base stations should be shared. However, data sharing between the moving cell and the fixed cell through the wireless backhaul not only requires additional use of radio resources, but also stable sharing of data may be difficult depending on radio channel conditions. Therefore, interference mitigation between the fixed cell and the moving cell based on cooperative communication may be difficult.

Referring to the bottom of FIG. 3, the channel between the moving cell and the fixed cell may change rapidly due to the movement of the moving cell. Therefore, there is a need to develop a technique for interference control and reduction in a situation in which signal and interference channel information sharing between cells is not smooth.

In such an environment, a technique of whitening may be used instead of interference avoidance through interference randomization or inter-cell interference averaging.

Inter-cell interference randomization is a method of randomizing interference from adjacent cells to approximate inter-cell interference to additive white Gaussian noise (AWGN). Inter-cell interference randomization may reduce the influence of the channel decoding process by another user's signal, for example, based on cell-specific scrambling, cell-specific interleaving, and the like.

Inter-cell interference averaging is a method of averaging all interferences by adjacent cells or averaging inter-cell interference at the channel coding block level through symbol hopping.

In the interference randomization scheme according to an embodiment of the present invention, when a desired signal is transmitted through a time / frequency / spatial resource, some resources may simultaneously receive a desired signal and an interference signal, and some resources may receive only a desired signal. The ratio between the desired signal and the interference signal for each resource is adjusted differently. As such, the channel coding gain may be obtained by changing the signal-to-interference / noise ratio (SINR) for each resource.

4 and 5 illustrate an interference mitigation method according to an embodiment of the present invention.

4 shows that the first base station A and the second base station B transmit signals to the first terminal a and the second terminal b, respectively. The signal transmitted from the first base station A may act as an interference signal to the second terminal b, and the signal transmitted from the second base station B may act as an interference signal to the first terminal a.

The first base station A and the second base station B may generate and transmit a signal in a resource pattern as shown by assigning a signal to be transmitted to time and frequency resources.

The first base station A allocates resources in the first pattern and transmits them to the first terminal a, and the second base station B allocates resources in the second pattern and transmits the resources to the second terminal b.

Even when the first base station A transmits a signal by allocating a resource in the first pattern, the resource allocation pattern received by the first terminal a by the signal generated by the second base station B is shown in FIG. Becomes pattern I of. Further, even when the second base station B transmits a signal by allocating a resource in the second pattern, the resource allocation pattern received by the second terminal b by the signal generated by the first base station A is shown in FIG. 4. Becomes pattern II at the bottom of.

Patterns I and II of FIG. 3 include a portion where a signal is received without interference and a portion where a signal and interference are simultaneously received. As described above, a method of randomizing interference by changing transmission energy for each resource has a disadvantage in that some resources cannot be used.

5 shows a signal transmission from two base stations to a terminal using a spatial domain.

As shown, the first base station A and the second base station B are transmitting signals using spatial diversity, and the signals transmitted from the first base station A and the second base station B are transmitted. The signal may be received as a desired signal instead of interference to each terminal (a, b), or may act as an interference signal.

The interference randomization scheme as shown in FIG. 5 consumes more energy than necessary, thereby degrading signal transmission efficiency.

In order to improve the disadvantages of the interference randomization of FIGS. 4 and 5, a method of performing interference randomization by increasing the variation of the interference signal received with the desired signal without changing the resource usage may be proposed. Can be.

Such an interference randomization technique is applicable to the transmitters performing spatial diversity transmission. The interference randomization is performed by differently setting a repetitive transmission pattern of repeated symbols for each base station in order to obtain spatial diversity gain. This is how it is done.

The improved interference randomization technique of the present invention diversifies the interference signals affecting the de-precoding of each symbol, and the signal to interference rate of the signal in quasi-static channel intervals. ) And to obtain interference diversity in the quasi-static channel interval in order to obtain diversity gain.

In general, signal diversity means equalization of reception power of a signal by repeatedly transmitting and receiving the same information through various channels. In the case of such signal diversity, signal to interference plus noise rate (SINR) fluctuation is reduced in the padding channel, thereby increasing the possibility of recovering information in the padding channel.

The interference diversity according to the present invention is similar in concept to signal diversity, and by receiving a plurality of interferences simultaneously through various channels, the reception power of the interference is leveled and the SINR variation due to the interference is reduced. As a result, the diversity gain of the signal is increased when the reception power of the interference signal is large.

As shown, the transmitting end receives one transmission symbol (S, first symbol) and the modified symbol (S *, second symbol) through different channels, for example, through a different antenna, such as a receiving end. Can be sent. In this case, the second symbol indicates that a complex conjugate operation is performed on the first symbol.

h0 represents a channel for a symbol between an antenna transmitting a first symbol and a receiving end, and h0 represents a channel for a symbol between an antenna transmitting a second symbol and a receiving end.

At this time, I represents an interference signal, and I * represents an interference signal calculated by complex conjugate. q0 represents a channel for the interference signal between the antenna and the receiving end transmitting the first symbol, q1 represents a channel for the interference signal between the antenna and the receiving end transmitting the q1 second symbol.

The first symbol and the second symbol may be allocated to a time, space or frequency resource and repeatedly transmitted, and the transmitting end may receive interference with a signal.

As shown, when the first symbol is transmitted, the receiving end together with the interference signal

Receives the second symbol for the second symbol.

Can be received.

Finally, the symbol received by the receiver and the interference signal may be represented by Equation 1.

Equation 1

If the channel state is a quasi-static state in which the channel hardly fluctuates, the interference diversity effect is reduced.

As shown, the terminal Rx, which is a receiving end, may receive a symbol S transmitted through two antennas, and may receive a signal transmitted through two antennas as an interference signal Z.

The first antenna 10 and the second antenna 20 may be antennas of a cell (hereinafter, referred to as a first cell) that provides a service to the terminal Rx, and the third antenna 30 and the fourth antenna 40. May be an antenna of a cell (hereinafter, referred to as a second cell) that transmits a symbol Z that may act as an interference signal to the terminal Rx.

For example, when a fixed cell serves as an interference source for a terminal serviced by a moving cell, the first cell may be a moving cell and the second cell may be a fixed cell. In contrast, the moving cell is served by the fixed cell. In the case of an interference source for the terminal, the first cell may be fixed and the second cell may be a cell moving cell.

In FIG. 7, a row for a symbol may mean a resource for transmitting a symbol such as time, space, or frequency.

In a semi-static state in which a predetermined interval channel is the same, the symbols S0 and S1... Are transmitted through the first antenna 10, and the modified symbols of the symbols transmitted through the first antenna 10 through the second antenna 20. The symbols S ₀ *, S ₁ * .. are transmitted.

The symbol Z ₀ , Z ₁ .. is transmitted through the third antenna 30, and the modified symbols Z ₀ *, Z ₁ * of the symbol transmitted through the third antenna 30 through the fourth antenna 40. .. is sent.

From the terminal's point of view, the transmission symbol S transmitted in the first cell may be a received signal, and the transmission symbol Z transmitted in the second cell may be an interference signal.

Thus, in FIG. 7, h ₀ is a channel between the first antenna 10 of the first cell and the terminal Rx serviced by the first cell, and h ₁ is the second antenna 20 and the first antenna of the first cell. The channel between the terminal Rx serviced by one cell, q ₀ is the channel between the third antenna 30 and the terminal Rx of the second cell, q ₁ is the fourth antenna 40 of the second cell and Represents a channel between the terminals (Rx).

Finally, the reception symbol received by the terminal (

) May be represented by Equation 2.

Equation 2

As shown in Equation 2, the coefficient of the interference signal acting as interference to the received symbol (

) Are two symbols (

), The SIR is the same for each symbol.

This may indicate that the gain for diversity of the entire packet is limited or reduced. If the interference is large in the quasi-static channel state, the UE may continue to receive strong interference.

Hereinafter, a description will be given of a method of ensuring interference diversity by changing a repetition pattern of interference symbols instead of interference of the same magnitude.

As shown in the figure, in a semi-static state in which the constant interval channel is the same, the symbols S ₀ , S ₁ , S ₂ , S ₃ .. are transmitted through the first antenna 10, and the second through the second antenna 20. The modified symbols S ₀ *, S ₁ *, S ₂ *, and S ₃ * .. of the symbol transmitted through one antenna are transmitted.

The symbol Z ₀ , Z ₁ , Z ₂ , Z ₃ .. is transmitted through the third antenna 30, and the modified symbol Z ₁ *, of the symbol transmitted through the third antenna through the fourth antenna 40. Z ₂ *, Z ₃ *, Z ₀ * .. are transmitted.

According to an embodiment of the present invention, the symbol transmitted through the fourth antenna is a cyclic shift (Cyclic shift) of the pattern in the existing Z ₀ *, Z ₁ *, Z ₂ *, Z ₃ *, Z ₁ *, Z ₂ *, Z ₃ *, Z ₀ * .. That is, the repetition pattern of symbols that may be interference signals to the terminal may be changed in a certain order.

The change of the repetition pattern may be implemented by using different precoders between the first cell and the second cell, which are transmission terminals.

When the pattern in which the symbol is repeated is changed, the received symbol (received by the terminal)

) May be represented by Equation 3.

Equation 3

As shown in Equation 3, the received symbol (

In the equation that acts as interference in), different interference symbols are included, which indicates that the interference changes for each symbol in the quasi-static period. Through this, it is possible to secure interference diversity for packets and to improve diversity performance.

According to the inter-cell interference mitigation method of FIG. 8, the base station may perform precoding by using different repetition patterns during symbol repetition. The upper left of FIG. 9 shows a pattern of a symbol generated by the first base station A as a precoding matrix, which can be expressed as Equation 4 or Equation 5 below.

Equation 4

Equation 5

As shown, the first base station A sequentially transmits a symbol S and a transform symbol S * thereof for the same signal through different antennas. That is, when symbol S ₀ is transmitted through one antenna, symbol S ₀ * is transmitted through another antenna. In addition, when the symbol S ₁ is transmitted through the antenna that transmits the symbol S0 sequentially, the symbol S ₁ * is transmitted through another antenna.

In contrast, the generated symbol pattern in the second base station B may be modified as shown in the upper right of FIG. 9. The second base station (B) has a period of 3 through two antennas, and may repeatedly transmit a symbol pattern by setting an offset in the order of transmitted symbols.

In the case of the symbol pattern generated by the second base station B, the number of symbols in which the pattern is repeated is 3, that is, the period is 3, and the offset of the transmission symbol sequence is set to one. That is, the symbols Z ₀ , Z ₁ , Z ₂ , Z ₃ .. are sequentially transmitted through one antenna, and the converted symbols for the symbols are Z ₀ , Z ₁ , Z ₂ , Z ₃ . Z ₁ *, Z ₂ *, Z ₀ *, Z ₄ *... It may be transmitted through other antennas in the same sequence.

If this is expressed as a precoding matrix, it can be expressed as in Equation 6.

Equation 6

Alternatively, the second base station B may generate a signal by applying a precoding in which the number of symbols in which the pattern is repeated is 3, that is, the period is 3, and the offset is set to 2 in the transmission symbol order. That is, the symbols Y ₀ , Y ₁ , Y ₂ , Y ₃ .. are sequentially transmitted through one of the antennas, and the converted symbols for the same are Y ₀ , Y ₁ , Y ₂ , Y ₃ . Y ₂ *, Y ₀ *, Y ₁ *, Y ₅ *... It may be transmitted through other antennas in the same sequence.

If this is expressed as a precoding matrix, it can be expressed as Equation (7).

Equation 7

The same or different offset may be applied for each cell, and the same or different period may be applied for each cell.

In addition, according to the period of the cyclic shift, cells using the same transmit antenna port may use different sizes of precoder.

For example, in Equation 6 or 7, the period of the cyclic shift in which the symbol is repeated is 3, but this may be 4 or more, and when the period is set, the offset value may be set to a maximum “period-1” value. have.

When precoding a signal is performed between cells which may be interference sources, a precoder matrix such as Equations 4 to 7 may be set in advance to variously change a pattern of a repeated symbol. Through this, interference diversity can be secured, thereby improving signal reception capability and preventing a situation in which performance of a received signal is degraded due to strong interference.

The first terminal (a) may receive an interference randomization effect by receiving Zn and Zmod (n + 1, 3), which are Sn and an interference signal, and the second terminal (b), Sn and Smod, which are Zn and an interference signal The interference randomization effect can be obtained by receiving (n + 2, 3) together.

Meanwhile, the closed loop MIMO technique described with reference to FIG. 1 has a disadvantage in that it does not operate when there is no information on interference or information on a channel through which an interference signal is propagated, and the interference random described with reference to FIGS. 8 and 9. This technique is disadvantageous when the closed-loop MIMO technique is used to transmit the desired signal.

Aha proposes a transmission scheme and a transmitter structure for using inter-cell interference randomization in a closed loop MIMO scheme for transmitting a desired signal.

The interference randomization technique described below may be applied to a moving cell or a closed femto cell performing downlink transmission between a small cell suitable for use of closed loop MIMO and a low speed mobile user. That is, according to an embodiment of the present invention, it is possible to overcome the interference between downlink cells caused by downlink transmission of a cell limited in information exchange with the small cell.

In a small cell environment in which a distance between a base station and a terminal is close, a high probability of generating a line of sight (LoS) is generated, which may mean that closed-loop MIMO transmission in the form of single layer beamforming occurs frequently. The inter-cell interference randomization described above is not suitable for the existing transmission end structure in which symbol repetitive transmission does not occur. The transmission end structure proposed in this embodiment is shown in FIG.

As shown, the transmitter includes a channel encoder 1010, a rank determiner 1015, a layer mapping unit 1020, a layer repeat and layer shift (LR & LS 1030), and a phase changer. (phase modifier 1040) and

precoders

1050, 1060.

The channel encoder 1010 encodes the input information bits according to a predetermined coding scheme to generate a codeword.

The channel encoder 1010 may further include a mapping unit for modulating each codeword according to a modulation scheme and mapping the codewords to modulation symbols having demodulation values. The modulation scheme is not limited, and may be m-PK (m-Phase Shift Keying) or m-Quadrature Amplitude Modulation (m-QAM). For example, m-PSK may be BPSK, QPSK or 8-PSK. m-QAM may be 16-QAM, 64-QAM or 256-QAM. The mapping unit generates modulation symbols for the codeword.

The rank determiner 1015 may determine the number of ranks based on the feedback information transmitted from the terminal.

The layer mapping unit 1020 maps modulation symbols of input codewords to each layer according to the number of layers. The layer may be referred to as an information path input to the

precoders

1050 and 1060 and may correspond to a value of rank. The layer mapping unit 140 may map modulation symbols of each codeword to each layer in correspondence to the number of layers determined from the rank determination unit 1015 (ie, rank).

If the rank is 1, the transmission sequence corresponding to this may be generated in the layer mapping unit 1020, and as shown, a transmission sequence for one layer L0 may be generated based on feedback information.

The generated transmission sequence is input to the LR & LS 1030, and the LR & LS 1030 repeatedly outputs the transmission sequence. Thus, although the rank is set to 1, the effect may be as if two layers are generated.

The LR & LS 1030 may repeat the transmission sequence for inter-cell interference randomization before the transmission sequence is mapped to the antenna port through precoding. The symbols of the transmission sequence may be repeated by the number of antenna port groups used for transmission diversity implementation and allocated to individual antenna port groups. The antenna port group may include a plurality of antennas, and the number of antenna port groups may mean a number corresponding to the number of precoders or the number of layers.

11A to 11C are diagrams for describing layer repetition and layer shift according to an embodiment of the present invention. 11A to 11C show a transmission sequence repeated according to this embodiment.

As shown in FIG. 11A, the transmission sequence S _1N ,... S ₁₂ , S ₁₁ , S _2N ... S ₂₂ , S ₂₁ generated by the channel encoder is as if two layers S are input to the LR & LS 1030. _1N ,... S ₁₂ , S ₁₁ and S _2N ... S ₂₂ , S ₂₁ ) can be expressed as being generated.

The transmission sequence represented by two layers (S _1N ,... S ₁₂ , S ₁₁ and S ₂₁ ,... S ₂₂ , S ₂₁ ) is repeated in the LR & LS 1030, and the repeated symbols are shifted at regular intervals within the transmission sequence. Can be.

The transmission sequence may be repeated by the number of antenna port groups. The order in which the repeated symbols are allocated to each antenna port group may be allocated to be mapped to an adjacent neighbor RE as shown in cell A at the top of FIG. 11A, or may be allocated to be spaced apart by one RE as shown in cell B at the bottom of FIG. 11A. . That is, the symbols in the repeated transmission sequence may be allocated to REs spaced apart by a predetermined number (K K is an integer).

In addition, as shown in FIG. 11A, a repetition pattern allocated to an antenna port group for each cell may be set differently to implement inter-cell interference randomization. Through this, inter-cell interference randomization can be obtained even in closed loop MIMO.

According to the embodiment of FIG. 11B, as shown in the upper part of FIG. 11B, a repeating pattern is allocated to cell A to be mapped to an adjacent neighbor RE, and one of the transmission sequences represented by two layers is input to cell B of the lower part of FIG. 11B. The transmission sequence Z _1N ,... Z ₁₂ , Z ₁₁ retain the first transmission pattern that was entered, and the other transmission sequences are Z _2N . Z ₂₂ and Z ₂₁ change a symbol's repetitive transmission pattern. The repeating pattern has period 3 and is cyclically shifted to offset 1.

Alternatively, according to the embodiment of FIG. 11C, a repetitive pattern is assigned to a cell A on the top so that a repetitive pattern is mapped to an adjacent neighbor RE, and one of the transmission sequences represented by two layers is maintained on the bottom cell B. , That is, the transmission sequence Z _1N ,... Z ₁₂ , Z ₁₁ maintain the first transmission pattern that was entered, and the other remaining transmission sequences Z _2N ... In Z ₂₂ and Z ₂₁ , the repeated transmission pattern of the symbol is changed as shown in FIG. 11B. Transmission sequence Z _2N ... Z ₂₂ and Z ₂₁ change the mapping of some symbols in the same pattern as the bottom of FIG. 11B. That is, in the pattern at the bottom of FIG. 11B, the position of the symbol Z12 is changed to Z22. The transmission pattern of the cell B of FIG. 11C may be an example in which the layer mapping is changed in units of symbols.

The phase change unit 1040 changes the phase of the repeated and shifted transmission sequence. As shown in the drawing, in order to obtain an effect of outputting two layers in a situation where the rank is determined as 1, orthogonality between layers should be guaranteed. The phase change unit 1040 generates an orthogonal sequence by changing the phase of the transmission sequence output to the two layers for orthogonality between the two layers.

As shown, the phase of the transmission sequence input to the first precoder 1050 is not changed, the phase of the transmission sequence input to the second precoder 1060 may be changed.

This orthogonal sequence may be allocated to time, frequency or spatial resources, and the phase changer 1040 may be implemented as an Alamouti transmitter. A transmission sequence input to the second precoder 1060 of FIG. 12 may be complexly computed or reversed in phase and allocated to spatial resources.

The

precoders

1050 and 1060 process the mapping symbols mapped to the respective layers by the MIMO method according to the plurality of antenna ports, and output antenna specific symbols. As shown, according to the present embodiment, there are two antenna port groups, and two layers are generated and output for a signal having a rank of one.

Referring to FIG. 13, when transmitting a repeated transmission sequence, a single antenna port group may be transmitted in the same manner as a single layer transmission without using different antenna ports.

This is possible because the phase change unit 1040 ensures orthogonality between the two layers.

The interference randomization scheme of the present invention guarantees a performance gain in the presence of unmeasured or unpredictable cell interference, and the existing scheme operates in the absence of such unknown inter-cell interference. Does not affect anything. That is, according to the present invention, the proposed scheme is applied only when the occurrence of unknown inter-cell interference is expected, otherwise it is not necessary to control the proposed scheme not to be applied.

Of course, the system may be designed to always use the interference randomization technique for signal transmission, or may be dynamically determined whether the technique is applied to be applied only in a specific case.

In this case, layer repetition and layer shift pattern in order to simplify the layer repetition and layer shift pattern of each cell, that is, to avoid signaling overhead of going through complex negotiations between cells so that each cell has a different repetition pattern from neighboring cells. Alternatively, the symbol repetition pattern is preferably set in advance.

According to an embodiment of the present invention, the layer repetition and layer shift pattern may be set according to the cell type.

For example, a repeating pattern is set according to a cell size such as a small cell or a micro cell, or a coverage overlapping with other cells such as a first layer and a second layer in a heterogeneous network. Accordingly, the repeating pattern may be set. Alternatively, a repeating pattern may be set according to the mobility of a cell, such as a moving cell and a fixed cell, or a repeating pattern may be set by a combination of the above examples.

If the symbol repetition pattern is set according to the cell size or the cell layer, continuous interference randomization is applied between cells that are likely to generate strong inter-cell interference in consideration of the magnitude of the inter-cell interference, which cannot be controlled by conventional interference avoidance. You can be prepared. In addition, when the symbol repetition pattern is set according to the mobility of the cell, it may correspond to the occurrence of unexpected inter-cell interference.

As shown, the first base station (A) and the second base station (B) each of the repeated symbols (repeated symbol) in the cells (①, ②) that are managed by each of the consecutive resource element (RE) Mapping.

Repeated symbols are shifted to offset 1 and allocated to resource elements in cells corresponding to the

small cells

③, ④, and ⑤.

Repeated symbols may be shifted to an offset 2 and mapped to resources allocated to the moving cell ⑥.

As such, the repetition pattern of the symbol may vary according to the size of the cell or the mobility of the cell, and the symbol pattern may be changed or newly set due to the offset adjustment of the repetition pattern.

Meanwhile, according to another embodiment of the present invention, the layer repetition and layer shift pattern may be set according to the cell ID. This means a method in which cells may have different symbol repetition patterns and may be implemented, for example, "repetitive offset = mod (PCID, K)".

According to another embodiment, when the layer repetition and layer shift patterns are set according to the above-mentioned cell type or cell ID, the layer repetition and layer shift patterns may be used in combination or after setting the layer repetition and layer shift pattern through these methods. A method of negotiating this may apply. That is, adjacent cells may negotiate a precoder to be used by each cell through higher layer signaling.

After setting an initial pattern to be used by each base station according to a cell type or a cell ID, if interference ranging between adjacent cells having the same pattern is required, negotiation between base stations is required. For example, if it is necessary to change the repetition pattern of a specific cell after the repetition pattern for each cell is set, each base station determines the repetition pattern change and notifies the base station of the neighboring cell by signaling the changed pattern, or A repeating pattern change may be requested by one base station to another base station through inter-base station signaling.

As shown, when the environment for requesting a pattern change occurs in the first base station A (S1510), for example, a pattern change request has been received from another base station or needs to be delivered to the second base station B for the change request. If there is, the first base station A may signal a recommended pattern list to the second base station B (S1520).

Upon receiving the recommendation pattern list, the second base station B determines whether to change the pattern (S1530), and notifies the first base station A of a response to whether the pattern is changed (S1540). The second base station B may transmit a response to the pattern change to the first base station A and information on the new pattern to the first base station A when it is determined that the pattern is to be changed (S1550).

The first base station A may select a precoder based on the new pattern (S1560) and perform pattern change according to the selected precoder. The first base station A having changed the pattern may transmit a message confirming this to the second base station B (S1570).

When the first base station A changes the repetition pattern of the symbol (S1610), the first base station A may signal the changed new pattern to the second base station B (S1620).

Upon receiving the signal for changing the pattern of the first base station A, the second base station B may recognize the pattern change of the first base station A (S1630) and perform a confirmation on the pattern change (S1640). )

The base station 800 includes a processor 810, a memory 820, and an RF unit 830. Processor 810 implements the proposed functions, processes, and / or methods. Layers of the air interface protocol may be implemented by the processor 810. The memory 820 is connected to the processor 810 and stores various information for driving the processor 810. The RF unit 830 is connected to the processor 810 to transmit and / or receive a radio signal.

The terminal 900 includes a processor 910, a memory 920, and an RF unit 930. Processor 910 implements the proposed functions, processes, and / or methods. Layers of the air interface protocol may be implemented by the processor 910. The memory 920 is connected to the processor 910 and stores various information for driving the processor 910. The RF unit 930 is connected to the processor 910 to transmit and / or receive a radio signal.

The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. The RF unit may include a baseband circuit for processing a radio signal. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means.

As described above, the present invention provides a method and apparatus for allowing a terminal to select a wireless node for uplink according to a predetermined condition when wireless connection is possible through different wireless networks.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. Also, one of ordinary skill in the art appreciates that the steps shown in the flowcharts are not exclusive, that other steps may be included, or that one or more steps in the flowcharts may be deleted without affecting the scope of the present invention. I can understand.

Claims

In the signal transmission method,

Determining a rank based on feedback information received from a terminal;

Generating a transmission sequence according to the rank;

Repeating the transmission sequence to generate a repeating transmission sequence and shifting a position of a symbol within the repeating transmission sequence;

Transmitting the transmission sequence and the repetitive transmission sequence.
The method of claim 1,

Changing the phase of the repeating transmission sequence with respect to the transmission sequence to generate orthogonality of the transmission sequence and the repeating transmission sequence.
The method of claim 1,

And the transmission sequence is repeated by the number of transmit antenna ports.
The method of claim 1,

The repeated symbols in the repeated transmission sequence are assigned to resource elements adjacent to each other.
The method of claim 1,

The repeated symbols in the repetitive transmission sequence are allocated to resource elements spaced apart by a predetermined number.
The method of claim 1,

The pattern of the repeated symbol in the repetitive transmission sequence is determined according to a cell ID.
The signal transmission device;

A signal transceiver;

A processor connected to the signal transceiver;

The processor determines a rank based on feedback information received from a terminal, generates a transmission sequence according to the rank, generates a repeated transmission sequence by repeating the transmission sequence, and shifts the position of a symbol in the repeated transmission sequence. Making a step; And transmit the transmission sequence and the repetitive transmission sequence.